The present invention relates to an electrophotographic printer utilizing an addressable image bar as the imaging device, and, more particularly, to a printer which utilizes a plurality of addressable image bars arranged generally linearly in an alternately staggered orientation.
The use of addressable image bars in an electrophotographic printing environment is known in the art. U.S. Pat. No. 4,386,836 discloses a printer in which a "optical writing unit" in conjunction with an imaging lens forms a latent image on a photoreceptor surface. The "optical writing unit" includes a light source which illuminates a liquid crystal shutter apparatus. Depending on the transmissivity of the individual shutters (which is set by a prescribed data input signal), light that passes through the shutter exposes the photoreceptor. U.S. Pat. No. 4,595,259 describes another printing system which includes a liquid crystal image bar which selectively transmits light into a lens so as to form latent electrostatic images a line at a time on a photoreceptor surface. The lens may be a conventional lens or a linear lens such as a Selfoc.TM. lens array.
U.S. Pat. No. 4,728,972 discloses the exposure of a xerographic drum through a liquid crystal bar controlled by a multiplexing driving circuit.
Also of interest as background for the use of liquid crystal bars in printers are the following articles: "Liquid Crystal Shutters For Printers" by M. Nagata and H. Nakamura, published in Mol. Cryst. Lic. Cryst., 1986, vol. 139, pages 143 to 160; and "How Liquid Crystal Shutters Are Used For Light Control In Non Impact Printers" by Y. Kawamura, published in Office Equipment and Products, vol. 13, December 1984, pages 60 to 66.
Another type of addressable image bar used in electrophotographic printers is disclosed, for example, in U.S. Pat. No. 4,477,175. As disclosed the image bar comprises a plurality of individually activated light emitting diodes (LEDs).
The image bars disclosed in the above patents and publications are linear substrates having an effective length equivalent to the width of the standard letter size document, e.g. 81/2 inches. As a general observation, the longer the image bar length, the greater the difficulty of manufacturing and the greater the cost. The reason for this is that the yield of these bars decreases exponentially with increased pixel density in active areas in a linear direction.